The present invention generally relates to the preparation of porous fibers. More particularly, the present invention provides a method of preparing a porous fiber from natural/synthetic polymer blends, to a porous fiber, and to a composition for use in preparing the fiber.
Polymer blending is a convenient method to develop products with desirable properties. The chemical and physical properties of the polymer blends are dependent on monomer type(s), molecular weight, and distribution of the respective polymers (Paul, D. R., Bucknall, C. B., Eds. Polymer blends; Wiley: New York, 2000). Most polymers are immiscible due to low entropy of mixing (Paul, D. R., Bucknall, C. B., Eds. Polymer blends; Wiley: New York, 2000; Flory, P. J. J. Chem. Phys., 10, 51 (1942); 3. Huggins, M. L. J. Chem. Phys., 9, 440 (1941)). Only through specific intermolecular interactions can favorable polymer blending occur and composite materials with desirable properties be produced. Nonetheless, a large number of technologically interesting polymers are multiphase inhomogeneous materials (Alexander-Katz, R. In Polymer blends; Paul, D. R.; Bucknall, C. B., Eds.; Wiley: New York, 2000, p 301-334). Properties such as prevention and control of gas and liquid permeation, gas and liquid adsorption/desorption and transmission and reflection of light are dependent on phase behavior, and more specifically on the size of the domains within the material.
Lignin, second only to cellulose in natural abundance, is an amorphous natural polymer existing in the cell wall of plants (Northey, R. A.; Glasser, W. G.; Schultz, T. P. Lignin: historical, biological, and materials perspectives; American Chemical Society: Washington, D.C., 2000). Its utilization in solid material systems is constrained by the extensive crosslinking, strong intramolecular interactions and high molecular weight of most lignins, which upon heating decompose rather than soften and flow. Attempts have been made, through polymer blending (Olabisi, O.; Robeson, L. M.; Shaw, M. T. Polymer-polymer miscibility; Academic Press: New York, 1979; Walsh, D. J.; Higgins, J. S.; Maconnachie, A.; North Atlantic Treaty Organization. Scientific Affairs Division. Polymer blends and mixtures; M. Nijhoff: Dordrecht; Boston, 1985; Meister, J. J.; Chen, M. J.; Milstein, O.; Gersonde, R.; Huttermann, A. Abstr. Pap. Am. Chem. Soc., 209, 116-PMSE (1995); Rials, T. G.; Wolcott, M. P. Journal of Materials Science Letters, 17, 317-319.(1998); Tan, T. T. M. Journal of Polymer Materials, 13, 195-199. (1996); Thring, R. W.; Vanderlaan, M. N.; Griffin, S. L. Biomass and Bioenergy, 13, 125-132.(1997); Wang, J. S.; Manley, R. S.; Feldman, D. Progress in Polymer Science, 17, 611-646.(1992); Li, Y.; Sarkanen, S. In Lignin: Historical, Biological, and Materials Perspectives; Amer Chemical Soc: Washington, 2000, p 351-366) or lignin derivatization (Li, Y.; Sarkanen, S. In Lignin: Historical, Biological, and Materials Perspectives; Amer Chemical Soc: Washington, 2000, p 351-366; Sudo, K.; Shimizu, K.; Nakashima, N.; Yokoyama, A. J. Appl. Polym. Sci., 48, 1485-1491.(1993); Kanazawa, K.; Koyama, M. Mokuzai Gakkaishi, 37, 869-873 (1991); Jain, R. K.; Glasser, W. G. Holzforschung, 47, 325-332 (1993); Glasser, W. G.; Jain, R. K. Holzforschung, 47, 225-233 (1993)), to alter the lignin""s viscoelastic properties and allow for flow. However, significant room for improvement remains in the art, particularly in the area of producing fibers from lignin.
Accordingly, there exists a need for compositions and methods that can be used, among other applications, in producing porous fibers in an economically and environmentally acceptable manner, such as through the use of an abundant material like lignin. The present invention addresses these and other needs in the art.
A method of preparing a porous fiber is disclosed herein. In one embodiment, the method comprises: (a) blending a natural polymer having a thermal stability with a synthetic polymer having a thermal stability, wherein the thermal stability of the natural polymer is different from the thermal stability of the synthetic polymer, and wherein the natural polymer and synthetic polymer form immiscible phases; (b) extruding the blended polymers while heating at a predetermined heating rate to a fiber spinning temperature; (c) spinning the fibers while maintaining the temperature; and (d) heating the fibers at a heating rate that maintains the natural polymer in a fiber form and that removes the synthetic polymer, whereby a porous fiber is formed. A porous fiber is also disclosed herein.
Optionally, the natural polymer is lignin. Also optionally, the synthetic polymer is a polyolefin, such as polyethylene or polypropylene. The natural polymer can optionally be present in an amount ranging from about 25% to about 99% by weight; and the synthetic polymer can optionally be present in an amount ranging from about 1% to about 75% by weight.
Accordingly, it is an object of the present invention to provide a method of preparing a porous fiber from natural/synthetic polymer blends, a porous fiber, and a composition for use in preparing the fiber. The object is achieved in whole or in part by the present invention.
An object of the invention having been stated herein above, other objects will become evident as the description proceeds when taken in connection with the accompanying Examples and Drawings as best described herein below.